1. Field of the Invention
The present invention generally relates to image forming apparatuses, erasing methods, and hard disk management methods, and more particularly to an image forming apparatus mounting a hardware disk, an erasing method for erasing information stored in the hard disk thereof, and a hard disk management method.
2. Description of the Related Art
Recently, an image forming apparatus (hereinafter, called multi-functional apparatus) accommodating functions of a facsimile, a printer, a copier, and a scanner into a single chassis has been widely known. In the multi-functional apparatus, a displaying part, a printing part, an imaging part, and a like are arranged within the single chassis, and also four applications corresponding to the facsimile, the printer, the copier, and scanner are included. By switching the four applications, the multi-functional apparatus operates as the facsimile, the printer, the copier, and the scanner.
There is a multi-functional apparatus mounting a hard disk (hereinafter, called HDD) for recording image data. In this case, this multi-functional apparatus conducts an erasing process for erasing data recorded in the HDD.
The erasing process takes a relatively large amount of time since the HDD recently becomes larger in addition to a large size of the image data. Accordingly, the erasing process for data recorded in the HDD influences other processes and then a performance of the multi-functional apparatus becomes degraded.
Moreover, if the multi-functional apparatus mounts the HDD, a security problem concerning information recorded in the HDD is raised. This security problem will be described with reference to FIG. 1 to FIG. 4.
FIG. 1 is a diagram showing magnetic data on the HDD and read data. The magnetic data on the HDD records data “0101010”. In the magnetic data on the HDD, flat portions show data “0” and convex portions show data “1”. In addition, a height of the convex portion shows a magnetic level.
In order to erase data recorded on the HDD, data “0” is overwritten on the HDD. A state of the HDD in this case is shown in FIG. 2. In FIG. 2, portions shown as “0 ERASE” become flat and show data “0”. On the other hand, other portions which are not shown as “0 ERASE” still remain parts of convex portions.
Accordingly, as shown in FIG. 2, by shifting position to read, the data “0101010” can be read.
Moreover, another method for erasing information by data “0” can be applied as shown in FIG. 3. FIG. 3 shows a state of the HDD which cannot be uniformly flat. In this case, if a read level is lowered to determine data “1”, the data “0101010” can be read.
As described above, even in a case in that data are regularly erased, data before erased can be read. Thus, data being accumulated and erased in the multi-functional apparatus can be read out.
As an example to avoid such problems described above, a method recommended by the NSA (National Security Agency) in U.S.A. will be described with reference to FIG. 4. In this method, random numbers are overwritten twice to the HDD and data “0” are overwritten once to the HDD.
It is assumed that data recorded on the HDD are “010101010101010”. Random numbers “010011000001000” are overwritten on the HDD, and then magnetic data at a first time are formed on the HDD. As shown in the magnetic data at the first time, portions overwriting “1” over “0” cannot be perfect convex portions, and portions overwriting “0” over “1” cannot be perfect flat portions. Next, random numbers “001111000010101” are overwritten on the HDD, and then magnetic data at a second time are formed on the HDD. Compared with the magnetic data at the first time, the magnetic data at the second time are different from the magnetic data at the first time.
Data “0” are further overwritten on the HDD, and then magnetic data at a third time are formed on the HDD. After that, it becomes quite difficult to predict original magnetic data.
As described above, the method for perfectly erasing information to maintain security of the information recorded in the HDD is disclosed. However, a method for practically realizing this method has not been introduced.
Furthermore, in a case that the HDD is mounted in the multi-functional apparatus, there is a disadvantage in that incomplete information remains in the HDD when the multi-functional apparatus is shout down while recording information such as image data to the HDD. In addition, the information being recorded when the multi-functional apparatus is shut down can be damaged.
The above-described phenomenon can occur while a regular operation is conducted. In this case, a consistency of information recorded in the HDD is lost.